Biofouling or biological fouling is the undesirable accumulation of microorganisms, algae, plants, and animals on wetted surfaces. It is found in almost all environments where aqueous liquids are in contact with other materials. The specific and non-specific interactions of proteins and cells with artificial surfaces form the basis of many medical, biochemical, and biotechnological applications. In order to prevent unwanted deposition (or biofouling), any non-specific protein and cell adsorption has to be suppressed. Preventing biological deposits of proteins or bacteria plays a key role in the field of hygiene and in keeping clean surfaces permanently. In addition, unwanted biological deposits on large wetted surfaces, such as ship hulls, water tanks, offshore rigs, etc., and in inaccessible places, such as large pipe systems, represent a major economic problem. Biofouling is on ship hulls, for example, can reduce the performance of the vessel in the water and increase its fuel consumption, which can significantly increase operating cost for ship owners and operators. As much as $50 billion in annual fuel saving has been realized by the shipping industry due to the use of antifouling coatings on ship hulls.
Conventional antifoulants are mostly toxic organometallic compounds or metals such as lead, arsenic, mercury, copper, tin, etc. These materials, however, can pose risks to the environment, and efforts have been made to find environmentally benign technologies.
The current antifouling technologies can be generally classified into four major categories: (1) biocidal antifouling paints containing a marine biocide, (2) non-biocidal electrical coatings, (3) non-biocidal antifouling paints, which almost exclusively function as fouling release, and (4) next generation fouling release products employing amphiphilic polymers or hydrogel materials to deter the settlement of microorganisms on a surface. Recently, hydrogel-forming coatings, in particular polyether-containing hydrogels, have been reported to be especially efficient in preventing marine fouling. Poly(ethyleneglycol) has been known to inhibit adhesion of protein “glue” secreted by the microorganism prior to establishing a thriving colony (see, for example, Merrill E. W., in Poly(ethylene glycol) Chemistry, Ed. J. M. Harris, pp 199-220, Plenum Press, New York: 1992; C.-G. Gilander, Jamea N. Herron, Kap Lim, P. Claesson, P. Stenius, J. D. Andrade, in Poly(ethylene glycol) Chemistry, Ed. J. M. Harris, Plenum Press, New York: 1992). U.S. Pub. No. 2005/0031793 and 2009/0029043 describe the syntheses of multifunctional star shaped polymers and their use for the preparation of thin hydrogel containing surface coatings to actively suppress unspecific protein adsorption.
Cruise et al. (Biomaterials 1998, 19, 1287-1294) and Han et al. (Macromolecules 1997, 30, 6077-6083.0) described the use of acrylate-terminated polymers produced either from the diols or triols of poly(ethyleneglycol) prepolymer for the production of hydrogel layers. The acrylate-terminated prepolymer was crosslinked either on its own or with acrylate-terminated glycerol triol in the presence of added benzyl dimethylketal to form a hydrogel. Hydrogel layers with thicknesses of 135 μm to 180 μm were obtained. Proposed applications for these hydrogel layers include their in vivo use, for example, to suppress post-operative adhesion, as diffusion barriers, for the bonding or sealing of tissues, for in vivo medicamentation and their use as a direct implant, e.g. in the form of a hydrogel cell suspension, peptide hydrogel or a growth factor hydrogel. M. A. Grunlan, et al. prepared siloxane tethered polyethylene glycol with a general formula, α-(EtO)3Si(CH2)2-oligodimethylsiloxanen-block-poly(ethylene glycol)-OCH3 via regioselective Rh-catalyzed hydrosilylation. The PEG tethered siloxane was subsequently crosslinked with silanol-terminated polydimethylsiloxane. The authors reported that the surface hydrophilicity and protein resistance increased with siloxane tether and that the flexibility of the siloxane sub-chains enabled the PEG to be more effectively mobilized to the surface (R. Murthy, C. D. Cox, M. S. Hahn, M. A. Grunlan, Biomacromolecules 2007, 8, 3244-3252). Grunlan, et al. further reported that such coatings are resistant to marine bacteria (Polymer Preprints 2011, 52(2) 1029).
Silicone antifouling products, i.e., non-biocidal or amphiphilic or hydrogel fouling release technologies, rely on the non-stick feature to discourage the attachment of marine organisms. Such technology is generally only effective when the coated vessel is moving above a certain minimum speed, and does not prevent fouling when the vessel is not in motion or moving slowly. Because of the non-stick nature, typical silicone fouling release coatings do not adhere well to anticorrosion coatings, typically an epoxy coating, that are used to coat the surface of an article such as a ship's hull. Strong adhesion is important to have sufficient coating durability. To overcome the poor adhesion of silicone to epoxy coatings, of a tie coat layer is employed between epoxy and silicone coating layers. However, the use of a tie coat increases the system cost in terms of materials and coating time, often adding an extra day of coating time for the additional coating.
Amphiphilic, silicone hydrogel antifouling coatings such as those described by Grunlan, employ small molecules of polyether-containing silanes to impart protein and marine bacterial resistance. However, the use of the polyether-containing silanes inhibits adhesion of silicone RTV to an epoxy coating.
U.S. Pat. Nos. 4,978,704 and 4,996,112 describe a one part RTV composition using a mixture of an aminosilane and an epoxysilane. U.S. Pub No. 2011/0250350 describes using aminosilanes mixed with silanol-terminated polydiorganosiloxane as a tie coat to improve adhesion. U.S. Pub. No. 2011/0250350 discloses adhesion improvement using bis(trialkoxysilyalky)amine and N,N′-bis(trialkoxysilylalkyl)alkylenediames in a silicone tie coat.
U.S. Pat. No. 6,723,376 describes a coating process using a curable silicon-containing functional group that is capable of latent condensation reaction to form an undercoat and followed by coating a curable polymeric fouling inhibiting material. The curing of the fouling inhibiting material bonds the top coat to the undercoat by condensation reaction with the curable silicon-containing functional groups in the undercoat. U.S. Pat. No. 5,691,019 discloses coating a fouling release layer onto an adhesion promoting anticorrosive layer, where the bonding of the fouling release layer to the anticorrosive layer is enabled by the incorporation of a curable aminosilicone fluid to the anticorrosive layer. The aminosilicone blooms to the interface between anticorrosive layer and fouling release layer to connect the two layers with respective chemical reactions of amines with epoxide of the epoxy layer and alkoxysilane with the silane or silanol of polydimethylsiloxane in the fouling release silicone layer. The incompatible nature of the aminosilicone in the epoxy formula helps the blooming of the aminosilicone. However, the incompatibility also drives up the requirement of the amount of aminosilicone. The aminosilicone molecules tend to aggregate into large globules sporadically scattering on the epoxy surface. Bonding can only occur at the sparsely area where aminosilicone globules cover. It typically requires a very large amount of aminosilicone to fully cover the epoxy surface in order to create sufficient bonding. As a result, the use of aminosilicone for adhesion is not efficient.